I found erros in ispConfig 3.0.5.2 cron
"PHP Warning: mysqli::mysqli(): Headers and client library minor version mismatch. Headers:50529 Library:100002 in /usr/local/ispconfig/server/lib/classes/db_mysql.inc.php on line 62"

This thread is quote outdated as mariadb is supported for a long time already. There are no problems with mariadb, all current setups (e.g. the latest ones for ubuntu, opensuse and centos) use all mariadb. Just ensure that you use the mariadb settings in my.cnf as described in the tutorials.

The tutorial that you followed install mysql and not mariadb, if you replace a package, then ypu will get errors off course. Mariadb is not 100% mysql compatible, thats why it requires some config settings in my.cnf file. St the line:

sql_mode=NO_ENGINE_SUBSTITUTION

in mysqld section of my.cnf file and restart mariadb.

Btw. the errr in your other post is not related to ispconfig at all, it just occurs because the php that you installed is not 100% compatible with the mysql replacement that you installed.